Phenylephrine is a selective α1-adrenergic receptor activator which results in the constriction of both arteries and veins.
It is a sympathomimetic drug, which means that it mimics the actions of epinephrine or norepinephrine.
Phenylephrine selectively binds to alpha-1 receptors which cause blood vessels to constrict.
Phenylephrine is primarily used as a decongestant, to dilate the pupil, to increase blood pressure, and relieves hemorrhoids.
When used orally as a decongestant, it relieves nasal congestion
Can be taken by mouth, as a nasal spray, given by injection into a vein or muscle, or applied to the skin.
Bioavailability is 38% through GI tract.
Protein binding 95%
Metabolism Liver
Onset of action
Very rapid (IV)
20 min by mouth.
Elimination half-life 2.1–3.4 h
Duration of action
Up to 20 min (IV).4 hrs by mouth
Common side effects include: nausea, headache, and anxiety.
Severe side effects may include a slow heart rate, intestinal ischemia, chest pain, kidney failure, and tissue death at the site of injection.
It is unclear if use during pregnancy or breastfeeding is safe.
Phenylephrine is used as a decongestant as an oral medicine or as a nasal spray.
It is a common ingredient in over-the-counter decongestants.
Phenylephrine’s efficacy as an oral decongestant has been questioned, with several independent studies finding that it provided no more relief to sinus congestion than a placebo.
Studies are available in support the efficacy of phenylephrine at a 10 mg dosage.
Its use on hemorrhoids is generally well tolerated.
Two studies examined the effects of phenylephrine on symptoms of allergic rhinitis by exposing people to pollen in a controlled, indoor environment: Neither study was able to distinguish between the effects of phenylephrine or a placebo.
The Food and Drug Administration withdrew the indication for the temporary relief of nasal congestion associated with sinusitis in 2007.
Phenylephrine can be used topically to prevent symptoms of hemorrhoids,
causing the constriction of vascular smooth muscle to narrow the swollen veins and relieve pain.
It is used as an eye drop to dilate the pupil to facilitate visualization of the retina.
Narrow-angle glaucoma is a contraindication to phenylephrine use.
As a mydriatic, phenylephrine is available in 2.5% and 10% minims.
It has been used as an injection into the anterior chamber of the eye to arrest intraocular bleeding occurring during cataract and glaucoma surgery.
It is commonly used as a vasopressor to increase the blood pressure in unstable patients with hypotension, especially resulting from septic shock: in anesthesia or critical-care practices.
it is useful to counteract hypotensive effect of epidural and subarachnoid anesthetics, as well as the vasodilating effect of bacterial toxins and the inflammatory response in sepsis and systemic inflammatory response syndrome.
Its elimination half life is about 2.5 to 3.0 hours.
A single intravenous bolus dose of phenylephrine is short lived and requires to be repeated every 10–15 minutes.
Because of its vasoconstrictive effect, phenylephrine can cause severe necrosis if it infiltrates the surrounding tissues.
It should be given through a central line if at all possible.
Damage may be prevented or mitigated by infiltrating the tissue with the alpha blocker phentolamine by subcutaneous injection.
Phenylephrine hydrochloride at 0.25% is used as a vasoconstrictor in some suppository formulations for hemorrhoids.
It has been used to treat conditions of orthostatic intolerance such as postural orthostatic tachycardia syndrome.
Phenylephrine diluted with normal saline and injected directly into the corpora cavernosa has been used for priapism: causing constriction of the blood vessels entering into the penis, thus causing decreased blood flow and relieving the priapism.
Phenylephrine side effects: hypertension, headache, reflex bradycardia, excitability, restlessness and cardiac arrhythmias.
Use is not suggested for use in patients with hypertension.
The medication is a sympathomimetic amine without beta-adrenergic activity, it does not increase contractility force and output of the cardiac muscle.
It may increase blood pressure resulting in a slow heart rate through stimulation of vascular baroreceptors.
During IV administration of phenylephrine commonly reflex bradycardia occurs.
Eye drops do not cause blood pressure changes at low dosage, and changes with the higher dose drops do not last long.
Phenylephrine can worsen prostatic hyperplasia can also be worsened by use, and chronic use can lead to rebound hyperemia.
Phenylephrine should be avoided by patients with a history of anxiety or panic disorders, or on anticonvulsant medication.
Phenylephrine drug interactions might produce seizures.
Some patients experience an upset stomach, abdominal cramping, and vomiting upon taking this drug.
Phenylephrine is pregnancy category C.
It is not known whether there is harm to the fetus.
Phenylephrine should only be given to pregnant women who have a clear need.
Extended use may cause rhinitis medicamentosa.
The hypertensive effect of phenylephrine may be increased by: monoamine oxidase inhibitors, tricyclic antidepressants, and hydrocortisone.
Agents that may decrease the effects of phenylephrine may include: calcium channel blockers, ACE inhibitors and benzodiazepines.
Pseudoephedrine causes both vasoconstriction and increase of mucociliary clearance through its nonspecific adrenergic activity.
Phenylephrine’s selective α-adrenergic agonism causes vasoconstriction alone, creating a difference in their methods of action.
Oral phenylephrine is extensively metabolized by monoamine oxidase.
Monoamine oxidase enzyme that is present on the mitochondrial membrane of cells throughout the body.